Acetolactate synthase (hereinafter referred to as “ALS”) is a rate-limiting enzyme in the biosynthetic pathway of branched chain amino acids, such as leucine, valine, and isoleucine, and is known as an essential enzyme for the growth of plants. ALS is also known to be present in a wide variety of higher plants. In addition, ALS has been discovered in various microorganisms, such as yeast (Saccharomyces cerevisiae), Escherichia coli, and Salmonella typhimurium. 
Three types of isoenzymes of ALS are known to be present in Escherichia coli and Salmonella typhimurium. Each of these isoenzymes is a hetero oligomer consisting of catalytic subunits with large molecular weights that govern catalytic activity of the enzyme and regulatory subunits with small molecular weights that function as feedback inhibitors through binding of branched-chain amino acids (Chipman et al., Biochim. Biophys. Acta. 1385, 401-419, 1998 [Non-patent document 1]). Catalytic subunits are located at the Ilv IH, Ilv GM, and Ilv BN operons, respectively. Also, ALS in yeast is a single enzyme consisting of a catalytic subunit and a regulatory subunit, as in the case of bacteria (Pang et al., Biochemistry, 38, 5222-5231, 1999 [Non-patent document 2]). The catalytic protein subunit is located at the locus ILV2.
In plants, ALS is known to consist of catalytic subunits and regulatory subunits, as in the case of the above microorganisms (Hershey et al., Plant Molecular Biology 40, 795-806, 1999 [Non-patent document 3]). For example, the catalytic subunits of ALS in tobacco (dicotyledon) are coded by two gene loci, SuRA and SuRB (Lee et al., EMBO J. 7, 1241-1248, 1988 [Non-patent document 4]); and those in maize are coded by two gene loci, als 1 and als 2 (Burr et al., Trends in Genetics 7, 55-61, 1991 [Non-patent document 5]; Lawrence et al., Plant Mol. Biol. 18, 1185-1187, 1992 [Non-patent document 6]). The nucleotide sequences of genes coding for catalytic subunits have been completely determined for dicotyledonous plants including tobacco, Arabidopsis, rapeseed, cotton, Xanthium, Amaranthus, and Kochia (See Chipman et al., Biochim. Biophys. Acta. 1385, 401-419, 1998 [Non-patent document 1] and International Publication WO97/08327 [Patent document 1]). However, maize and rice are the only monocotyledonous plants for which nucleotide sequences have been completely determined.
Meanwhile, herbicides, such as sulfonylurea herbicides, imidazolinon herbicides, triazolopyrimidine herbicides, and pyrimidinyl carboxy herbicides (hereinafter referred to as “PC herbicides”), are known to suppress plant growth by inhibiting ALS (Ray, Plant Physiol. 75, 827-831, 1984 [[Non-patent document 7]; Shaner et al., Plant Physiol. 76, 545-546, 1984 [Non-patent document 8]; Subramanian et al., Plant Physiol. 96, 310-313, 1991 [Non-patent document 9]; and Shimizu et al., J. Pestic. Sci. 19, 59-67, 1994 [Non-patent document 10].
Plants with one or two nucleotide substitutions in a gene coding for ALS, which induce one or two amino acid substitutions in a region conserved among different species, are known as plants having resistance to these herbicides. Examples of such a gene include a gene coding for ALS having strong resistance to sulfonylurea herbicides (see Kathleen et al., EMBO J. 7, 1241-1248, 1988 [Non-patent document 11]; Mourad et al., Planta, 188, 491-497, 1992 [Non-patent document 12]; Guttieri et al., Weed Sci. 43, 175-178, 1995 [Non-patent document 13]; Bernasconi et al., J. Biol. Chem. 270, 17381-17385, 1995 [Non-patent document 14]; and JP Patent Publication (Kokai) No. 63-71184 A (1988) [Patent document 2]); a gene coding for ALS having strong resistance to imidazolinon herbicides (see Mourad et al., Planta, 188, 491-497, 1992 [Non-patent document 12]; Lee et al., FEBS Lett. 452, 341-345, 1999 [Non-patent document 15], and JP Patent Publication (Kokai) No. 5-227964 A (1993) [Patent document 3]); a gene coding for ALS having strong resistance to PC herbicides (see WO02/44385A1 [Patent document 4] and WO03/083118A1 [Patent document 5]); and a gene coding for ALS having resistance to sulfonylurea, imidazolinon, and PC herbicides (see Kathleen et al., EMBO J. 7, 1241-1248, 1988 [Non-patent document 11]; Bernasconi et al., J. Biol. Chem. 270, 17381-17385, 1995 [Non-patent document 14]; Hattori et al., Mol. Gen. Genet. 246, 419-425, 1995 [Non-patent document 16]; Alison et al., Plant Physiol. 111, 1353, 1996 [Non-patent document 17]; Rajasekarau et al., Plant Sci. 119, 115-124, 1996 [Non-patent document 18]; JP Patent Publication (Kokai) No. 63-71184 A (1988) [Patent document 2]; JP Patent Publication (Kokai) No. 4-311392 A (1992) [Patent document 6]; Bernasconi et al., U.S. Pat. No. 5,633,437, 1997 [Patent document 7]; WO02/44385A1 [Patent document 4]; and WO03/083118A1 [Patent document 5]).
The production of a plant that exerts resistance to both sulfonylurea and imidazolinon herbicides has been attempted by crossing a plant having ALS that exerts resistance specifically to sulfonylurea herbicides with a plant having ALS that exerts resistance specifically to imidazolinon herbicides (Mourad et al., Mol. Gen. Genet, 243, 178-184, 1994 [Non-patent document 19]). Furthermore, artificial alteration of a gene coding for ALS into a herbicide resistance gene has been attempted (see Ott et al., J. Mol. Biol. 263, 359-368, 1996 [Non-patent document 20]; JP Patent Publication (Kokai) No. 63-71184 A (1988) [Patent document 2]; JP Patent Publication (Kokai) No. 5-227964 A (1993) [Patent document 3]; and JP Patent Publication (Kohyo) No. 11-504213 A (1999) [Patent document 8]). It has thus been revealed that a single amino acid deletion causes ALS to exert resistance to both sulfonylurea and imidazolinon herbicides (see JP Patent Publication (Kokai) No. 5-227964 A (1993) [Patent document 3]).
As described above, ALSs having resistance to herbicides and genes coding for ALSs have been aggressively studied. However, no cases have been reported to date concerning a mutant ALS gene having resistance specifically to PC herbicides alone using resistance to PC herbicides as an indicator. If a mutant ALS gene having specific resistance to a specific herbicide is obtained, such mutant ALS gene can be used for various applications. No cases have been reported to date concerning such mutant ALS gene, which is useful in terms of specificity to PC herbicides.
Non-patent document 1 Chipman et al., Biochim. Biophys. Acta. 1385, 401-419, 1998
Non-patent document 2 Pang et al., Biochemistry, 38, 5222-5231, 1999
Non-patent document 3 Hershey et al., Plant Molecular Biology 40, 795-806, 1999
Non-patent document 4 Lee et al., EMBO J. 7, 1241-1248, 1988
Non-patent document 5 Burr et al., Trends in Genetics 7, 55-61, 1991
Non-patent document 6 Lawrence et al., Plant Mol. Biol. 18, 1185-1187, 1992
Non-patent document 7 Ray, Plant Physiol. 75, 827-831, 1984
Non-patent document 8 Shaner et al., Plant Physiol. 76, 545-546, 1984
Non-patent document 9 Subramanian et al., Plant Physiol. 96, 310-313, 1991
Non-patent document 10 Shimizu et al., J. Pestic. Sci. 19, 59-67, 1994
Non-patent document 11 Kathleen et al., EMBO J. 7, 1241-1248, 1988
Non-patent document 12 Mourad et al., Planta, 188, 491-497, 1992
Non-patent document 13 Guttieri et al., Weed Sci. 43, 175-178, 1995
Non-patent document 14 Bernasconi et al., J. Biol. Chem. 270, 17381-17385, 1995
Non-patent document 15 Lee et al., FEBS Lett. 452, 341-345, 1999
Non-patent document 16 Hattori et al., Mol. Gen. Genet. 246, 419-425, 1995
Non-patent document 17 Alison et al., Plant Physiol. 111, 1353, 1996
Non-patent document 18 Rajasekarau et al., Plant Sci. 119, 115-124, 1996
Non-patent document 19 Mourad et al., Mol. Gen. Genet, 243, 178-184, 1994
Non-patent document 20 Ott et al., J. Mol. Biol. 263, 359-368, 1996
Patent document 1 International Publication WO97/08327
Patent document 2 JP Patent Publication (Kokai) No. 63-71184 A (1988)
Patent document 3 JP Patent Publication (Kokai) No. 5-227964 A (1993)
Patent document 4 International Publication WO02/44385
Patent document 5 International Publication WO03/083118
Patent document 6 JP Patent Publication (Kokai) No. 4-311392 A (1992)
Patent document 7 Bernasconi et al., U.S. Pat. No. 5,633,437
Patent document 8 JP Patent Publication (Kohyo) No. 11-504213 A (1999)